Know the Science: How Medications and Supplements Can Interact
Drugs With a Narrow Therapeutic Range
Having the right amount of certain drugs in your body is crucial. If the amount of the drug is even a little too low or too high, it can cause big problems.
Drugs like these are said to have a “narrow therapeutic range” or “narrow therapeutic index.”
Interactions are of special concern for drugs with a narrow therapeutic range.
| Examples of Drugs With a Narrow Therapeutic Range |
|---|
| Carbamazepine (used to prevent seizures) |
| Cyclosporine (used to prevent organ transplant rejection) |
| Digoxin (used to treat heart problems) |
| Levothyroxine (used to treat thyroid problems) |
| Phenytoin (used to prevent seizures) |
| Warfarin (an anticoagulant—also called a blood thinner) |
If you’re taking a dietary supplement, and your health care provider prescribes a drug with a narrow therapeutic range, what should you do?
Tell your health care provider that you’re taking the supplement and ask the provider what you should do.
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